1. Field of the Invention
The present invention relates to a process for manufacturing auto parts from polyurethane materials.
2. Description of the Prior Art
Recently the reaction-injection molding process has come into increasing use for the fabrication of auto parts such as bumpers, grills, soft fascias, steering wheels with foamed or non-foamed urethane. The reasons for this are that polyurethane fully meets the necessary requirements of auto parts that they be resistant to shock and chemicals. The reaction-injection molding process is suitable for molding objects of intricate configurations such as exist in various auto parts, because in this process, polyurethane can be blended under pressure and at the same time can be injected into a metal mold. Moreover, the molding cycle of polyurethane is extremely short and occurs with high molding efficiency.
Polyurethane, however, has certain well-known deficiencies which include the fact that it is not sufficiently weatherproof. For instance over a period of long service life, the exterior portions of auto parts made from polyurethane will be exposed to direct sunlight. Under these conditions not only will the surface of the part loose its gloss and crack, but the interior portions thereof will suffer physical deterioration. The addition of carbon black to the polyurethane articles will promote the effective absorption of ultraviolet rays and therefore is seemingly a logical solution to the problem of weathering. However, the problem with this approach is that the color of carbon black will fade with time. In an effort to improve the weathering problem of polyurethane auto parts various anti-aging agents for rubber have been proposed, but with no satisfactory results obtained for auto parts which are subjected to long service life. Therefore a need continues to exist for a method of improving the weathering resistance of polyurethane to improve its acceptability for use in the manufacture of atuo parts.